1. Field of the Invention
The present invention relates generally to a stocking system for loading and unloading cassettes containing substrates and, more particularly, to a stocking system having improved mechanisms to store and transfer cassettes.
2. Discussion of the Related Art
A stocking system is a storage system to handle work pieces, and is generally used in manufacturing lines for liquid crystal display (LCD) devices.
LCD devices are used in clocks, calculators, monitors of personal computers, notebooks, aviation instruments, and portable personal appliances. A typical liquid crystal display panel of the LCD device includes a TFT (thin-film transistor) array substrate and a color-filter array substrate coupled together at a constant cell gap and a liquid crystal material filled in the cell gap between the two substrates.
Manufacturing processes of the liquid crystal display device may be generally divided into array, cell, and module processes.
A glass substrate is the most commonly utilized substrate for the liquid crystal display panel. The glass substrate is loaded in a box, commonly called as a cassette, and transported to manufacturing equipment for individual processes. The glass substrates of the liquid crystal display panels may be transported or returned in sequence or in a group from one manufacturing apparatus to another in the manufacturing processes.
The stocking system is a system that loads, stores, and unloads a plurality of the cassettes containing substrates manufactured in a unit process or cassettes containing substrates to be supplied to a unit process.
FIG. 1 is a schematic top view illustrating a stoker system according to the related art.
As illustrated in FIG. 1, the related art stocking system 10 comprises a first shelf line 11 storing a plurality of cassettes, a second shelf line 12 parallel to the first shelf line 11 at a designated interval, and an automated crane 13 located between the first shelf line 11 and second shelf line 12 to transport the cassettes.
To store a plurality of the cassettes, individual shelf lines 11 and 12 have a plurality of loading spaces arranged horizontally in rows, and stacked on top of each other. Each loading space has a floor.
The automated crane 13 transports the cassettes to a given position in the stocking system. The automated crane 13 includes a crane arm 14, which moves horizontally at a given stroke toward the shelf lines 11 and 12 so as to load/unload the cassettes to/from the shelf lines 11 and 12.
However, the related art stocking system may have the following disadvantages.
Firstly, because the related art stocking has only one crane, an entire manufacturing line may stop when the crane is out of order or is otherwise undergoing maintenance.
Secondly, because the related art stocking has only one crane, increasing the number of cassettes to be transported per unit time may overload the crane, thereby delaying cassette-handling times.
Finally, the crane arm of a related art stocking is designed to have a limited stroke in the horizontal direction and operate only with the shelf lines installed on the both sides of the crane. When additional shelf lines are installed adjacent to the existing shelf lines to increase cassette-storing capacity, the crane arm cannot reach the added shelf lines.